Synthesis and structure of some azo coupled cyclic β-enaminones

Article abstract of DOI:10.1002/mrc.1975

The reaction of 3-phenylaminocyclopent-2-en-1-one with 4-methyl, 4-methoxy and 4-chlorobenzenediazonium tetrafluoroborates was used to prepare the azo coupling products 3a-c. It was found that these compounds are present in both CDCl₃ solution

Full text of DOI:10.1002/mrc.1975

MAGNETIC RESONANCE IN CHEMISTRY
Magn. Reson. Chem. 2007; 45: 330–339
Published online in Wiley InterScience
(
www.interscience.wiley.com) DOI: 10.1002/mrc.1975
Synthesis and structure of some azo coupled cyclic
b-enaminones†
1
∗
1
1
2
3
ˇ
Petr Sim u˚ nek, Lucie Luskov a´ , Mark e´ ta Svobodov a´ , Valerio Bertolasi, Anton ´ı n Ly cˇ ka
and Vladim ´ı r Mach a´ cˇ ek1
1
2
3
ˇ
University of Pardubice, Department of Organic Chemistry, N a´ m. Cs. Legi ´ı 565, CZ-532 10, Pardubice, Czech Republic
Universit a` di Ferrara, Dipartimento di Chimica and Centro di Strutturistica Diffrattometrica, Via L.Borsari 46, I-441 00 Ferrara, Italy
Research Institute for Organic Syntheses (VUOS), Rybitv ´ı 296, CZ-532 18 Pardubice 20, Czech Republic
Received 8 November 2006; Revised 9 January 2007; Accepted 10 January 2007
The reaction of 3-phenylaminocyclopent-2-en-1-one with 4-methyl, 4-methoxy and 4-chlorobenzenedia-
zonium tetrafluoroborates was used to prepare the azo coupling products 3a-c. It was found that
these compounds are present in both CDCl solution and solid phase practically exclusively as (E)-3-
3
phenylamino-2-(4-subst.phenyldiazenyl)cyclopent-2-en-1-ones with N–H· · ·N intramolecular hydrogen
bond. The substitution of the phenyl residue of the diazonium salt has no effect on the position of the
tautomeric equilibrium. On the other hand, the compounds 4a, b formed by the reaction of 3-phenylamino-
1
3
H-inden-1-one with 4-methylbenzene- or benzenediazonium tetrafluoroborates exist in CDCl solution
and in solid phase as hydrazone compounds. In the solution they occur as a mixture of three forms,
out of which two were identified as E/Z isomers with different types of hydrogen bonds. Compound
5
formed by the reaction of 3-amino-5,5-dimethylcyclohex-2-en-1-one with 4-methoxybenzenediazonium
solution; this
tetrafluoroborate is converted into a stable hydrochloride 5·HCl on standing in CHCl
3
product exhibits a high degree of delocalization of the positive charge. Its structure was studied by means
of X-ray. Copyright  2007 John Wiley & Sons, Ltd.
KEYWORDS: H; 13C; 15N; X-ray; tautomerism; enaminones; diazonium salts; azo coupling
1
INTRODUCTION
was shifted virtually completely to the hydrazone tautomer
regardless of the substitution in the diazonium salt. If the
molecule of starting enaminone contained a primary amino
group, the proportion of azo form substantially increased,
and the azo form was even predominating if, at the same
time, the diazonium salt contained a 4-methoxy group.
The azo coupling reactions with cyclic enaminones other
than derivatives of 3-amino-5,5-dimethylcyclohex-2-en-1-
one have not been studied so far. The five-membered ring
differs considerably from the six-membered one in the exis-
tence of eclipsed conformations and in the higher tendency
to form exocyclic double bonds. The impact of these differ-
ences on the structure of azo coupling products obtained
from enaminones derived from cyclopentan-1,3-dione and
indane-1,3-dione is dealt with in the present paper.
The reaction of 3-amino or 3-phenylamino-5,5-dimethyl-
cyclohex-2-en-1-ones with substituted benzenediazonium
tetrafluoroborates in CH Cl in the presence of sodium
2 2
acetate gives products of double azo coupling reaction
at positions 2 and 4 (Scheme 1, Ref. 1) even if equimolar
amounts of the enaminone and diazonium salt are used. In
contrast to the derivatives of 3-amino-5,5-dimethylcyclohex-
2
-en-1-one, the azo coupling reactions with enaminones
derived from pentane-2,4-dione only give products of
reaction of one enaminone molecule with one diazonium salt
2
,3
molecule (with a single known exception of azo coupling
4
reaction with 4-dimethylaminopent-3-en-2-one ). Reasons
for the different behavior of cyclic and acyclic enaminones
are not known.
The position of the azo-hydrazone tautomeric equilib-
rium at C(4) carbon atom in the products of the azo coupling
reaction with derivatives of 3-amino-5,5-dimethylcyclohex-
RESULTS AND DISCUSSION
Azo coupling reaction products from
2
3
-en-1-one in CDCl solution depended predominantly
3
-phenylaminocyclopent-2-en-1-one
on the substitution of the amino group in the starting
enaminone: with the N-aryl derivatives the equilibrium
There are three (or even four, if also the amino group is taken
into account: positions 2-, 4- and 5- on the cyclopentene ring)
potential sites of attack by diazonium ion in the molecule
of starting enaminone 1, in analogy with the enaminones
studied earlier (Refs 1–5).
Ł
ˇ
Correspondence to: Petr Sim u˚ nek, University of Pardubice,
ˇ
´
Department of Organic Chemistry, N a´ m. Cs. Legiı 565, CZ-532 10,
Pardubice, Czech Republic. E-mail: petr.simunek@upce.cz
†
The ORTEP view of compound 3a formed by reac-
tion of the enaminone 1 with 4-methylbenzenediazonium
Dedicated to Prof. Jarom ´ı r Kav a´ lek on the occasion of his 70th
birthday.
Copyright  2007 John Wiley & Sons, Ltd.

Azo coupled ˇ-enaminones
331
Scheme 1. Reaction of dimedone enaminones with diazonium salts.
Table 1. Hydrogen bond parameters ( A˚ , °) for compound 3a
and 4b
2.60–2.64 A˚ (Refs 3,5), in compounds where C1 C2 is not
included in any ring. From the bond numbers, given in
Table 2, can be observed an asymmetrical delocalization
within the heterodienic system, greater on the enamino frag-
ment C1 C2–N3 than on the diazenyl group C1–N2 N1.
This situation can be accounted for as a supplementary
delocalization due to the presence of the superimposed
enaminone system HN3–C2 C1–C5 O1. The crystal pack-
ing is characterized by weaker intermolecular C–HÐ Ð ÐO
hydrogen bonds (Table 1).
On the basis of 15N NMR (Table 3, Fig. 2) it was found
that compound 3a exists in CDCl3 solution practically
exclusively as (E)-2-(4-methylphenyldiazenyl)cyclopent-2-
en-1-one, which stands in accord with the tautomeric form
of this substance in crystalline form.
D–HÐ Ð ÐA
D–H
DÐ Ð ÐA
HÐ Ð ÐA
D–HÐ Ð ÐA
3
a
–
–
–
–
136(2)
145(1)
169(2)
–
N3–H3Ð Ð ÐN1
C4–H41Ð Ð ÐO1
0.90(2)
0.98(2)
0.93(3)
–
2.683(2) 1.96(2)
3.408(2) 2.56(2)
3.363(3) 2.44(3)
a
b
C12–H121Ð Ð ÐO1
4
b
–
–
N1–H1Ð Ð ÐN3
N3–H3Ð Ð ÐN1
C15–H15Ð Ð ÐO1
0.96(2)
2.750(2) 2.01(2)
132(2)
0.92(17) 2.750(2) 2.11(19) 126(14)
1.00(2) 3.218(2) 2.53(2) 126(1)
c
a
1
/2 C x, 1/2 ꢀ y, z.
b
c
ꢀ
x, ꢀy, 1 ꢀ z.
1
ꢀ x, 1 ꢀ y, ꢀz.
Also, the nitrogen atoms in 4-methoxy derivative 3b and
1
5
4
-chloro derivative 3c exhibit the N chemical shifts very
similar to those of compound 3a (Table 3), which means
that all the three substances exist in their CDCl solutions
tetrafluoroborate is shown in Fig. 1. In analogy with
the enaminones studied earlier (Refs 1–5) azo coupling
took place at CH carbon of the enaminone grouping
3
as the azo forms, and the azo-hydrazone equilibrium is not
even affected by the presence of electron-acceptor chlorine
substituent in substance 3c.
O
C–CH C–NH. The molecule displays an intramolec-
ular N3–HÐ Ð ÐN1 resonant assisted hydrogen bond (RAHB)
between the enamino and diazenyl systems (Table 1). The
inclusion of C1 C2 double bond in a five-membered ring
gives rise to geometrical constraints that hinder the shorten-
If the structure of azo coupling products obtained from
3
-phenylaminocyclopent-2-en-1-one is compared with that
of products obtained from analogous enaminones with six-
membered ring, then substantial differences become obvious:
6
ing of the hydrogen bond. Accordingly, the intramolecular
N1Ð Ð ÐN3 distance of 2.683(2) A displays a significant length-
˚
ž the reaction with 3-phenylaminocyclopent-2-en-1-one at
ening with respect to the same distances, in the range
otherwise the same reaction conditions (solvent, base,
Copyright  2007 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2007; 45: 330–339
DOI: 10.1002/mrc

ˇ
˚
332
P. Simunek et al.
Figure 1. The ORTEP view of compound 3a. Thermal ellipsoids are drawn at 30% probability level.
Table 2. Bond distances ( A˚ )/Bond numbers and Bond Angles
°) for compound 3a and 4b
Table 3. 15N NMR parameters of the compounds 3a–c a 4a,b
in CDCl3
(
1
1
15
3
a
Jꢀ N ,
3
1
d
Hꢁ /
Bond distances/Bond numbers
N1–N2
N1–C6
C1–N2
15
Jꢀ N1,
1.275(2)/1.70
1.420(2)/1.00
1.383(2)/1.14
1.397(2)/1.50
C1–C5
O1–C5
N3–C2
N3–C13
1.449(2)/1.19
1.222(2)/1.84
1.328(3)/1.58
1.412(2)/1.01
N1a
N2a
N3a
1
Hꢁ
e
3a
3b
3c
4a-A
4a-B
4a-C
4b-A
4b-B
49.8
55.3
46.2
95.6
92.1
98.8
ꢀ19.2
ꢀ17.0
ꢀ242.4
ꢀ247.7
ꢀ242.4
ꢀ74.7
–
86.4
–
87.6
94.2
96.1c
C1–C2
Bond angles
N2–N1–C6
N1–N2–C1
N2–C1–C2
N2–C1–C5
C2–C1–C5
b
115.3(1)
114.7(1)
129.7(1)
120.5(1)
109.8(1)
N3–C2–C1
N3–C2–C3
C1–C2–C3
C2–N3–C13
–
122.5(1)
126.4(1)
111.0(1)
132.7(1)
–
ꢀ202.2
ꢀ208.4
N2 D ꢀ25.2, J D 95.1
ꢀ203.9
ꢀ210.8
ꢀ19.8
ꢀ72.9
94.2b
96.1b
–
–
b
4
b-C
N1 D ꢀ209.4, J D 96.2
4
b
a
b
c
For numbering see Schemes 2 and 3.
Taken from F2 axis projection of 2D spectrum.
Taken from 1D H– N spectrum.
For compounds 3a–c.
Bond distances/Bond numbers
N1–N2
1.322(2)/1.37
1.400(2)/1.05
1.304(2)/1.69
1.466(2)/1.11
C1–C5
O1–C5
N3–C2
N3–C10
1.474(2)/1.07
1.221(2)/1.84
1.285(2)/1.86
1.420(2)/1.00
1
15
N1–C16
d
e
C1–N2
For compounds 4a, b.
C1–C2
Bond angles
N2–N1–C16
N1–N2–C1
N2–C1–C2
N2–C1–C5
C2–C1–C5
118.3(1)
118.9(1)
130.1(1)
120.3(1)
109.5(1)
N3–C2–C1
N3–C2–C3
C1–C2–C3
C2–N3–C10
–
121.4(1)
132.4(1)
106.2(1)
122.7(1)
far as we know, this is the first case where the azo cou-
pling reaction product obtained from an enaminone with
N-phenyl group exists in the form of pure azo compound
(Scheme 2).
The yields of compounds 3 are low (15–26%). All our
temperature) only gives products of a single azo coupling
process, even in the cases where the molar ratio of
diazonium salt to enaminone is 2 : 1.
attempts at improving the yields failed. The diazonium salt
is decomposed into tarry products during the azo coupling
reaction, and in the case of preparation of compound 3b
we identified anisole. Obviously, the azo coupling reaction
is accompanied by redox reactions with the diazonium ion
acting as the oxidant.
ž the azo coupling products obtained from 3-phenylamino-
cyclopent-2-en-1-one exist as practically pure azo com-
3
pounds in both the CDCl solution and solid phase. As
Copyright  2007 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2007; 45: 330–339
DOI: 10.1002/mrc

Azo coupled ˇ-enaminones
333
Figure 2. 500 MHz H–15N gsHMBC spectrum of the compound 3a in CDCl3.
1
of these NH protons it can be presumed that they repre-
1
3
sent isomers with various hydrogen bonds. The C NMR
spectrum indicates the presence of three carbonyl groups.
1
5
From the υꢀ Nꢁ values (Table 3) it is obvious that both the
predominating products (A, B) are hydrazone compounds,
which is also confirmed by the values of their coupling
1
1
15
constants Jꢀ H, Nꢁ (Table 3). The suggested structures of
both major forms (A, B) are presented in Schemes 3 and 4.
In order to assign the structures to the individual forms,
we used the stereochemical dependence between the cou-
pling constants Jꢀ N, Cꢁ – Scheme 4 (Ref. 7). On the basis
of the values of these coupling constants it is presumed that
the major form A is isomer (E, E) with the intramolecular
hydrogen bond N–HÐ Ð ÐN. The second form is isomer (Z, E)
with the intramolecular hydrogen bond N–HÐ Ð ÐO C. The
information that we could obtain about the third product
Scheme 2. Reaction of 1 with diazonium ion.
Azo coupling reaction products from
-phenylamino-1H-inden-1-one
The proton NMR spectrum of product 4a obtained from azo
coupling reaction of 4-methylbenzenediazonium tetrafluo-
roborate and 3-phenylamino-1H-inden-1-one (2) indicates
2
15
13
3
3
that this substance in CDCl solution exists as a mixture of
three forms (A–C) in approximate ratios 30 : 6 : 1. No chem-
ical exchange between these forms is observed on the NMR
time scale. The above mentioned ratio is not much changed
by a change in solvent (being 26 : 9 : 1 in DMSO), and also
it remains unchanged after repeated recrystallizations of the
product from various solvents (ethanol, cyclohexane). The
(
constituting less than 2.8%) from the spectra of the sample
with natural isotope abundance was not sufficient for deter-
mining its structure (Table 3). Owing to the similarity of its
NMR parameters with the parameters of the other forms
(A, B) we suggested the structure of the C as (Z, Z) isomer
Schemes 3 and 4. Compound 4b shows similar behavior to
that of the 4-methyl derivative 4a (Fig. 3).
1
15
1
D H– N HMBC spectrum shows that all the three forms
contain NH protons. With regard to the chemical shifts
Copyright  2007 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2007; 45: 330–339
DOI: 10.1002/mrc

ˇ
˚
334
P. Simunek et al.
The ORTEP view of compound 4b is shown in Fig. 4. In
the crystalline state this structure consists of a mixture of two
tautomeric imino-hydrazone and enamino-diazenyl forms
in the ratio 89 : 11; accordingly the tautomeric equilibrium is
shifted toward the imino-hydrazone form while in the similar
compound 3a, only the enamino-diazenyl system is present.
This tautomerism is probably related to the rotation of the
phenyl ring, C10–C15, which prevents the ꢂ-delocalization
ascribed to the steric hindrance of the phenyl ring belonging
to the indandione fragment.
With respect to compound 3a, the proton transfer
produces a lengthening of N1Ð Ð ÐN3 hydrogen bond distance
˚
up to 2.750(2) A while, within the heterodienic ring, the
double bonds are mainly localized on C1 N2 and C2 N3
bonds. The conjugation through the N3 C2–C1 N2–N1H
system is due both to the RAHB effect and by the
superimposition of the two tautomeric forms and is more
pronounced within the hydrazone fragment owing to the
through the N3–C10 bond. Such conformation, as showed
by the C2–N3–C10–C11 D ꢀ80.2ꢀ2ꢁ° torsion angle, can be
Scheme 3. Reaction of 2 with diazonium ion.
Scheme 4. Structures 4a A–C and recognition between the forms 4a-A and 4a–B.
Copyright  2007 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2007; 45: 330–339
DOI: 10.1002/mrc

Azo coupled ˇ-enaminones
335
Figure 3. 500 MHz H–15N gsHMBC spectrum of the compound 4b in CDCl3.
1
presence of the ketonic group C5 O1 which enhances
the delocalization along the further heterodienic system
O1 C5–C1 N2–N1H.
To our knowledge, compounds 4a and 4b are the second
described case of the hydrazone compound obtained from
azo coupling reaction with enaminone that exists as a mixture
3
of several forms in CDCl solution. The first instance was
described in Ref. 5 A common feature of both these cases is
the presence of phenylimino group adjacent to phenyl group.
If there was a carbonyl group instead of the phenylimino
group in the neighborhood of the phenyl group, then only
5
one form of azo coupling product was observed (Scheme 5).
Structure of product 5·HCl in solid phase
The six-member cyclic enaminones derived from dimedone
react with two molecules of diazonium salt to give products
1
of double azo coupling (Scheme 1). Product 5 (Scheme 1),
obtained from the reaction of 3-amino-5,5-dimethylcyclohex-
2
-en-1-one with 4-methoxybenzenediazonium tetrafluorob-
orate forms a stable hydrochloride on standing in chloroform
solution; its solid phase structure is presented in Scheme 6.
The stability of this hydrochloride can be explained by dis-
tinct delocalization of its positive charge. With regard to this
Scheme 5. Relationship between the structure of azo coupling
product and number of forms.
Copyright  2007 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2007; 45: 330–339
DOI: 10.1002/mrc

ˇ
˚
P. Simunek et al.
336
Scheme 6. Solid state structure of 5 · HCl.
stabilization, it can be deduced that the free base 5 exhibits
considerable basicity.
8
ž
The ORTEP view of compound 5 HCl is shown in
Fig. 5. The protonated organic cation displays an extended ꢂ-
delocalization through the moiety including all the nitrogen
atoms, which can be evidenced by the bond order values
9
Figure 4. ORTEP view of compound 4b. Thermal ellipsoids are
drawn at 40% probability level. Both tautomeric hydrogens
linked to N1 and N3 atoms, are displayed.
reported in Table 4. Pauling’s bond order or, more exactly,
bond number, n, is evaluated by the formula dꢀnꢁ D
dꢀ1ꢁ ꢀ c log n, where d(n) and d(1) are the bond lengths
for n D n and 1, respectively, and c is a constant to be
evaluated for each type of chemical bond. The pure single
and double bond distances have been retrieved from Ref. 10.
The partial double bond character exhibited by the N1–N2,
N2–C1, N4–N5, N4–C5 and N3–C6 bonds is indicative that
the positive charge is mainly shared on the N1–H, N5–H2
and N3–H2 groups.
The overall molecular conjugation and the intramolecular
hydrogen bonds tend to maintain the structure almost planar.
The strength of N1–HÐ Ð ÐO1 intramolecular hydrogen bond
[
N1Ð Ð ÐO1 D 2.619ꢀ3ꢁ A] is determined both by resonance
˚
Figure 5. ORTEP view of compound 5·HCl. Thermal ellipsoids
1
1–13
assisted hydrogen bond (RAHB)
ˇ-enaminone system, O1 C2–C1 N2–N1H, and by the
positive partial charge on N1–H moiety.
effects within the
are drawn at 30% probability level.
The other short intramolecular interactions N3–HÐ Ð ÐN2
Table 5. Hydrogen bond parameters ( A˚ , °) for compound
5 · HCl
and N3–HÐ Ð ÐN4 involving the enamino N3–H
2
group,
cannot be considered true hydrogen bonds, because the
D–HÐ Ð ÐA
D–H
DÐ Ð ÐA
HÐ Ð ÐA
D–HÐ Ð ÐA
N–HÐ Ð ÐN angles of 104(2) and 106(2)° are too far from
linearity, but only electrostatic interactions which contribute
significantly to the stability of the overall organic cation.
The intermolecular hydrogen bonds, given in Table 5,
N1–H1NÐ Ð ÐO1
0.90(3)
0.87(2)
0.90(3)
0.82(3)
0.82(3)
0.87(2)
0.90(3)
0.90(4)
0.92(2)
0.93(3)
1.00(3)
0.93(3)
2.619(3)
2.92(2)
2.78(1)
2.647(2)
3.176(2)
2.572(2)
3.323(2)
3.330(3)
3.695(2)
2.96(1)
1.88(3)
2.40(3)
2.32(3)
2.32(2)
2.49(2)
2.19(3)
2.62(3)
2.43(4)
2.80(2)
2.46(3)
2.48(4)
2.61(2)
139(2)
118(2)
111(2)
104(2)
142(2)
106(2)
136(2)
174(3)
164(2)
113(2)
123(2)
155(2)
N3–H31NÐ Ð ÐO1B
a
N1–H1NÐ Ð ÐO1B
2 3
involve N1–H, N5–H, N3–H groups and CHCl solvent
N3–H32NÐ Ð ÐN2
N3–H32NÐ Ð ÐCl1
N3–H31NÐ Ð ÐN4
Table 4. Selected Bond distances ( A˚ )/Bond numbers and
Bond Angles (°) for compound 5 · HCl
b
N5–H5NÐ Ð ÐCl1
C23–H23Ð Ð ÐCl1
C14–H14Ð Ð ÐCl1
Bond distances/Bond numbers
N1–N2
N1–C9
N2–C1
C1–C2
C2–O1
C1–C6
1.293(2)/1.57
1.406(3)/1.02
1.337(2)/1.44
1.447(3)/1.20
1.230(2)/1.78
1.439(2)/1.26
N3–C6
C5–C6
N4–C5
N4–N5
N5–C16
–
1.310(2)/1.64
1.459(2)/1.14
1.308(2)/1.66
1.313(2)/1.43
1.409(2)/1.01
–
a
C10–H10Ð Ð ÐO1B
b
C8–H81Ð Ð ÐO1B
3.14(1)
3.477(4)
c
C10–H10Ð Ð ÐO1A
a
2
ꢀ x, ꢀy, 1 ꢀ z.
b
c
1 ꢀ x. y, 1 ꢀ z.
x C 1, y C 1, z.
Bond angles
N2–N1–C9
N1–N2–C1
N2–C1–C2
N2–C1–C6
N3–C6–C1
N3–C6–C5
121.0(2)
119.7(2)
125.2(2)
114.7(2)
119.6(2)
119.3(2)
C1–C6–C5
N4–C5–C6
N4–C5–C4
N5–N4–C5
N4–N5–C16
–
121.0(2)
111.0(2)
129.5(2)
124.1(2)
119.4(2)
ꢀ
molecule as donors, while the chloride anion Cl and the
disordered water molecule act as acceptors. The network
of intermolecular hydrogen bonds in the crystal packing
is sustained by intermolecular C–HÐ Ð ÐX (X O, Cl) weaker
interactions.
Copyright  2007 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2007; 45: 330–339
DOI: 10.1002/mrc

Azo coupled ˇ-enaminones
337
O
N
NMR spectroscopy
The NMR spectra were measured at laboratory tempera-
N
N
X
N2 BF4
H
O
N
ture using the following spectrometers: Bruker AMX 360
AcONa
CH2Cl2
1
13
+
(360.14 MHz for H, 90.57 MHz for C and 36.50 MHz for
O
N
O
N
H
N
N
X
15
X
H
N
H
N) equipped with a 5-mm broad-band probe and Bruker
N
X+
1
13
Avance 500 (500.13 MHz for H, 125.77 MHz for C and
1
5
5
0.69 MHz for N) equipped with a 5-mm broad-band probe
with a magnetic field gradient in the direction of the z axis
and with a 5-mm triple resonance probe with a magnetic field
gradient in the direction of the z axis. Proton NMR spectra
Scheme 7. Summary of the reaction of some cyclic five
membered ˇ-enaminones with diazonium salts.
measured in CDCl
ane as the internal standard for H (υ 0.05) and in DMSO-d
3
were calibrated on hexamethyldisilox-
CONCLUSIONS
1
6
on the central signal of the solvent multiplet (υ 2.55). The
C NMR spectra were calibrated on the central signal of the
The ring size reduction of starting enaminone results in a
marked change in behavior to diazonium ion. In contrast
to six-member cyclic enaminones, 3-phenylaminocyclopent-
1
3
solvent multiplet (υ D 39.6 for DMSO-d
6
and υ D 76.9 for
1
5
CDCl
3
5
). The N NMR spectra were calibrated on external
2
4
-en-1-one (1) only reacts with one molecule of 4-methyl,
-methoxy or 4-chlorobenzenediazonium tetrafluoroborate,
1
neat N nitromethane placed in coaxial capillary (υ D 0.0).
The individual proton signals were assigned by H,H-
COSY spectra.
this being the case even if the ratio of reacting components
was 2 : 1 in favor of the diazonium salt. The azo coupling reac-
tion products 3a–c obtained from 3-phenylaminocyclopent-
The carbon NMR spectra were measured in the standard
way and by means of the APT pulse sequence (spectral width
2
-en-1-one (1) exist practically exclusively in the tautomeric
2
6.455 kHz, acquisition time 1.238 s, zero filling to 64 k and
form enamino-azo (Scheme 7), while in all the cases of
enaminones with N-aryl group studied so far the stable
tautomeric form was arylimino-hydrazone. The virtually
pure azo compound of the product 3a obtained by azo
coupling reaction of 4-methylbenzenediazonium tetraflu-
oroborate and 3-phenylaminocyclopent-2-en-1-one (1) was
also proved by X-ray analysis in solid form.
line broadening 1 Hz prior to Fourier transformation). The
assignment of the individual signals was carried out by
1
13
means of 2D gs H– C HMQC (experiment performed with
the CH coupling 145 Hz, 2 k ð 128 zero filled to 2 k ð 1 k,
sinebell squared in both dimensions) processed in phase
1
13
sensitive mode and gs H– C HMBC (experiment performed
with the long-range CH coupling 6–10 Hz, 2 k ð 160 zero
filled to 2 k ð 1 k, sinebell squared in both dimensions)
processed in magnitude mode.
The reaction of 3-phenylamino-1H-inden-1-one (2) with
4
-methylbenzenediazoniumandbenzenediazoniumtetraflu-
oroborates produces practically pure hydrazone compounds
a and 4b (Scheme 7), respectively, in spite of the fact that
The nitrogen chemical shifts were measured by indirect
4
1
15
detection gs H– N HMBC processed in the magnitude
mode. The gradient ratios were 70 : 30 : 50.1. Experiments
were processed with NH one bond coupling 90 Hz and NH
long-range coupling 5 Hz, 2 k ð 160 zero filled to 2 k ð 1 k,
sinebell squared in both dimensions. The values of coupling
the extent of the conjugated system would be larger if these
substances existed in the enamino-azo form. Apparently,
the conjugation in the phenylimino-hydrazone system is
more significant than the potential conjugation with the
annellated benzene ring. Analogous reasons (increase in the
significance of conjugation in the oxo-hydrazone grouping
1
5
1
1
15
constants Jꢀ N, Hꢁ were read from 1D H– N HMBC
spectra optimized for 90 Hz. The pulse programs were taken
from Bruker software library.
O
C–C N–NH to the detriment of the conjugation with
annellated ring) probably change the equilibrium in favor of
the hydrazone form in the series of azophenol, azonaphthol,
azoanthranol (Refs 14–19).
Another difference between the structures of azo cou-
pling reaction products obtained from the two types of
enaminones 1 and 2 studied is the fact that the compounds
X-ray structure determinations
The crystal data for compounds 3a and 5 · HCl were collected
at room temperature (T D 295 K) and those for compound
4
b at low temperature (T D 120 K), using a Nonius Kappa
CCD diffractometer with graphite monochromated Mo-
K˛ radiation and corrected for Lorentz and polarization
effects. The structures were solved by direct methods (SIR97
3
with annellated benzene ring exist in CDCl solution as
mixtures of three forms, out of which two were identified
as geometrical isomers with different arrangement and dif-
ferent types of intramolecular hydrogen bonds. Like in the
earlier studied azo coupling reaction products from enam-
inones, in this case, too, the isomers with intramolecular
bond —NHÐ Ð ÐN are predominant.
[
Ref. 20]) and refined using full-matrix least-squares. In
compound 5 · HCl all nonhydrogen atoms were refined
anisotropically and hydrogens isotropically, except for the
hydrogens of the disordered water molecule, which were not
localized in the difference Fourier maps. The chlorine atoms
3
of CHCl molecule were found disordered and refined over
two independent orientations with occupancies of 0.5. The
asymmetric unit contains a disordered molecule of water,
which was refined over two positions O1A and O1B with
occupancies of 0.8 and 0.2, respectively.
In compounds 3a and4b all nonhydrogen atoms were
refined anisotropically and hydrogens isotropically. In 4b
EXPERIMENTAL
General
The melting points were measured on a Kofler hot stage
microscope and were not corrected. The elemental analyses
were carried out on an automatic analyzer FISONS EA 1108.
Copyright  2007 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2007; 45: 330–339
DOI: 10.1002/mrc

ˇ
˚
338
P. Simunek et al.
the difference Fourier map showed diffuse electron density
between N1 and N3 atoms with two maxima from which two
proton positions could be identified. Refinement of the two
tautomeric H atoms with partial occupancy and isotropic
thermal parameters fixed at 1.2 times the average of those of
the related nitrogen atoms was successfully attempted giving
the final occupancy factors of 89% for H1 and 11% for H3.
All the calculations were performed using SHELXL-
Cyclopentane-1,3-dione and indane-1,3-dione were pur-
chased commercially and were used without any changes.
Sodium nitrite (95% N),a commercial product, was
bought from Aldrich.
1
5
3
-Phenylaminocyclopent-2-en-1-one (1)
A mixture of 38 mmol cyclopentan-1,3-dione and 38 mmol
aniline was heated in 30 ml toluene to boiling point for 4 h.
The water formed was azeotropically distilled off, and the
solvent was continuously replenished by fresh toluene. Then
the reaction mixture was cooled and the separated product
9
7 [Ref. 21] and PARST [Ref. 22] implemented in WINGX
[
Ref. 23] system of programs. The crystal data and refinement
parameters are summarized in Table 6. Selected interatomic
distances and angles are given in Tables 2 and 4. Hydrogen
bond parameters are reported in Tables 1 and 5.
was collected by suction and recrystallized from DMF. Yield
1
6
5%. m.p. 236–239 °C. (Ref. 24 m.p. 235–236 °C). H NMR
Complete crystallographic data (excluding structural fac-
tors) for the structures in this paper have been deposited
at the Cambridge Crystallographic Data Centre and allo-
cated the deposition numbers CCDC 609 534, 609 535 and
(
5
(
3
3
500.13 MHz, CDCl ): υ 2.27–2.29 (2H, m), 2.75–2.77 (2H, m),
.44 (1H, s), 7.13–7.15 (1H, m), 7.22–7.23 (2H, m), 7.40–7.42
13
2H, m), 9.70 (1H, s). C NMR (125.77 MHz, CDCl
3
): υ 28.8,
3.2, 101.1, 120.5, 124.1, 129.7, 140.6, 172.9, 205.1.
6
09 536. Copies of the data can be obtained, free of charge via
WWW.ccdc.cam.ac.uk/conts/retrieving.html or on applica-
tion to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [fax:
C44(0)-1223-336033 or e-mail: deposit@ccdc.cam.ac.uk].
2
5
3
-Phenylamino-1H-inden-1-one (2) (Ref. )
A reaction flask with magnetic stirrer was charged with
4 mmol indane-1,3-dione (4), a six-fold molar amount of
1
dimethylformamide and 10% molar excess of aniline with
respect to indane-1,3-dione. With continuous stirring, 8 ml
glacial acetic acid was added drop by drop within 10 min.
The reaction product began to separate gradually. After
half an hour, water was added to the reaction mixture and
stirring was continued for 1 h. The separated green solid was
Material
Dichloromethane was purchased dry commercially from
Fluka and stored over molecular sieves. Anhydrous sodium
acetate was remelted on a porcelain dish and left to cool in a
desiccator.
The diazonium tetrafluoroborates were prepared by a
known procedure.1
collected by suction and washed with ether. The product
was recrystallized from toluene, m.p. 219–221 °C (Ref. 25
1
°
C). Yield 67%. H NMR (360.14 MHz, DMSO): υ
Table 6. Crystal data
213–215
5
.33 (1H, s), 7.24–7.26 (1H, m), 7.39–7.56 (7H, m,), 7.91–7.92
Compound
Formula
3a
4b
5·HCl
13
(
1H, m), 9.95 (1H, s). C NMR (90.57 MHz, DMSO): υ 93.1,
C
119.1, 119.8, 122.1, 124.8, 129.5, 130.3, 131.2, 134.5, 139.3,
39.7 161.1, 193.2.
C18H17N3O C21H15N3O ꢀC22H26N5O3ꢁ
ꢀ
Cl ÐCHCl3ÐH2O
M
291.35
325.36
581.31
General procedure of azo coupling reaction with
3
System
Space group
Monoclinic Monoclinic Triclinic
P21/a
-phenylaminocyclopent-2-en-1-one
P21/a
P - 1
A 100 ml Erlenmeyer flask was charged with 3-phenylamino-
cyclopent-2-en-1-one (2 mmol), dichloromethane (20 ml),
sodium acetate (6 mmol) and the respective benzenediazo-
nium tetrafluoroborate (2 mmol). The reaction mixture was
stirred at r.t. 24 h. The separated solid was collected by
suction, washed with dichloromethane, and the combined
filtrates were evaporated until dry. The evaporation residue
was purified by chromatography and recrystallization. The
following compounds were prepared in this way:
˚
a/A
9.2417(2)
10.9532(7) 9.3236(1)
˚
b/A
17.5978(6) 13.5031(9) 11.3595(2)
9.8341(4)
90
110.622(1) 102.492(4) 95.9688(6)
90
˚
c/A
/°
11.1039(8) 14.7434(3)
90 92.4669(6)
˛
ˇ/°
ꢃ/°
90
112.413(1)
1429.89(4)
2
3
˚
U/A
Z
1496.88(9) 1603.4(2)
4
1.293
295
0.83
4
ꢀ
3
Dc/g cm
T/K
ꢄ/cm
1.348
120
0.85
1.350
295
4.51
3
-Phenylamino-2-(4-methylphenyldiazenyl)cyclopent-2-
ꢀ
1
en-1-one (3a)
Âmin ꢀ Âmax/°
3.90–29.92 2.80–26.05 3.26–28.00
The evaporation residue was purified by chromatography on
silica gel, first using ethyl acetate and subsequently acetone
Unique Refl.ns
Rint
4296
0.028
3169
3130
0.029
2383
6874
0.018
5031
as the mobile phases. The product is orange crystalline solid,
Observed Refl.ns
I > 2ꢅꢀIꢁ]
1
m.p. 182–183 °C. Yield 26%. H NMR (500.13 MHz, CDCl
):
3
[
υ 2.37 (3H, s), 2.55–2.59 (2H, m), 2.89–2.92 (2H, m), 7.20–7.25
4H, m); 7.29–7.32 (1H, m), 7.42–7.46 (2H, m), 7.68–7.70 (2H,
R (Obs. Refl.ns)
wR (All Refl.ns)
S
ꢆmax;
ꢆmin/e A
0.0492
0.1436
1.039
0.0404
0.1000
1.065
0.0522
0.1681
1.042
(
1
3
m), 12.94 (1H, s). C NMR (125.77 MHz, CDCl
2.2, 83.2, 121.4, 123.1, 126.8, 129.6, 137.7, 139.8, 149.7, 164.5,
167.6, 198.7. Anal. calc. for C H N O (291.35): C 74.20; H
3
): υ 21.3, 24.0,
3

0.24;–0.15 0.14,–0.17 0.39;–0.31
ꢀ
3
1
8
17
3
˚

5
.88; N 14.42; found C 74.28; H 5.93; N 14.38.
Copyright  2007 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2007; 45: 330–339
DOI: 10.1002/mrc

Azo coupled ˇ-enaminones
339
3
2
-Phenylamino-2-(4-methoxyphenyldiazenyl)cyclopent-
-en-1-one (3b)
7.26–7.29 m, 7.32–7.35 m, 7.44–7.49 m, 7.86 d, J D 7.4 Hz,
1
3
3
14.34 brs. ( C NMR, 125.77 MHz, CDCl ): υ 115.68, 118.92,
Chromatography silicagel/acetone. Yield 15%. m.p. 174.5–
123.45, 124.73, 124.90, 125.66, 129.15, 129.45, 130.57, 132.23,
1
1
2
75 °C. H NMR (500.13 MHz, CDCl
.88–2.91 (2H, m), 3.83 (3H, s), 6.90–6.92 (2H, m), 7.23–7.26
3
): υ 2.54–2.56 (2H, m),
133.49, 135.89, 139.53, 141.64, 148.72, 159.81, 186.38. Form B
1
( H NMR, 500.13 MHz, CDCl
3
): υ 6.67–6.68 m, 6.95–6.97 m,
(
2H, m), 7.27–7.30 (1H, m), 7.41–7.45 (2H, m), 7.75–7.77 (2H,
6.99–7.02 m, 7.15–7.18 m, 7.36–7.39 m, 7.60–7.63 m, 7.70–
7.73 m, 7.80–7.83 m, 8.08–8.09 m, 13.23 brs. ( C NMR
1
3
13
m), 12.76 (1H, s). C NMR (125.77 MHz, CDCl
3
): υ 24.0, 32.2,
5.5, 114.1, 123.0, 123.1, 126.7, 128.4, 129.7, 137.5, 146.2, 160.9,
64.0, 198.6. Anal. calc. for C18 (307.35): C 70.34; H
.58; N 13.67; found C 70.53; H 5.64; N 13.41.
5
1
5
125.77 MHz, CDCl
124.64, 128.54, 128.97, 132.07, 134.75, 136.37, 141.27, 143.35,
151.79, 155.10, 188.43. Anal. calc. for C21 O (325.36): C
7.52; H 4.65; N 12.91; found C 77.24; H 4.89; N 12.63.
3
): υ 114.96, 118.32, 122.40, 122.56, 122.89,
17 3 2
H N O
15 3
H N
7
3
-Phenylamino-2-(4-chlorophenyldiazenyl)cyclopent-2-
3
-Amino-4-(4-methoxyphenyldiazenyl)-5,5-
en-1-one (3c)
dimethylcyclohex-3-ene-1,2-dione
-(4-methoxyphenylhydrazone) (5) was prepared by a
The crude evaporation residue was washed with ethylacetate
and then recrystallized from ethanol. Yield 15% brown
2
1
known procedure (Ref. 1)
crystalline solid. m.p. 153–157 °C. H NMR (500.13 MHz,
CDCl ): 2.53–2.55 (m, 2H), 2.88–2.90 (m, 2H), 7.23–7.25 (m,
H), 7.30–7.34 (m, 3H), 7.43–7.46 (m, 2H), 7.66–7.69 (m, 2H),
A single crystal of hydrochloride 5·HCl was prepared by
3
stepwise evaporation of chloroform solution of compound
2
1
1
1
1
3
5.
2.77 (s, 1H). C NMR (125.77 MHz, CDCl
22.61, 123.18, 127.07, 128.76, 129.06, 129.69, 134.89, 137.09,
50.22, 164.71, 198.50. Anal. calc. for C17 O (311.77):
3
): 23.90, 32.13,
Acknowledgements
The authors (P.S., L.L., M. S., V. M.) acknowledge the financial
support by the Ministry of Education, Youth and Sports, of the
Czech Republic (project No. MSM 002 162 7501).
H14ClN
3
ˇ
C 65.49; H 4.53; N 13.48; found C 65.29; H 4.61; N 13.62.
3
2
-Phenyliminoindan-1,2-dione
-(4-methylphenylhydrazone) (4a)
REFERENCES
A 100 ml Erlenmeyer flask was charged with 3-phenylamino
H (4.5 mmol), dichloromethane (20 ml), sodium acetate
13.5 mmol) and 4-methylbenzenediazonium tetrafluorob-
orate (4.5 mmol). The reaction mixture was stirred at r.t.
4 h. The solid portion was collected by suction, the filter
ˇ
˚
1
2
. Simunek P, Ly cˇ ka A, Mach a´ cˇ ek V. Eur. J. Org. Chem. 2002; 2764.
1
(
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ˇ
˚
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4
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2
2002; 642: 41.
ˇ
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. Simunek P, Bertolasi V, Ly cˇ ka A, Mach a´ cˇ ek V. Org. Biomol.
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cake was washed with dichloromethane, and the combined
filtrates were evaporated until dry. The evaporation residue
was thoroughly washed with a mixture of n-hexane-ethyl
acetate 2 : 1. The undissolved portion was recrystallized
from ethanol. The product is a yellow crystalline solid,
m.p. 171–173 °C. Yield 40%. Form A ( H NMR, 500.13 MHz,
CDCl
ˇ
˚
. Simunek P, Bertolasi V, Pe sˇ kov a´ M, Mach a´ cˇ ek V, Ly cˇ ka A. Org.
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6. Bertolasi V, Gilli P, Ferretti V, Gilli G. Acta Crystallogr., Sect. B
1994; 50: 617.
7. Kalinowski H-O, Berger S, Braun S. 13C NMR Spektroskopie.
Georg Thieme Verlag: Stuttgart, 1984; 517.
1
3
): υ 2.31 s, 6.58–6.62 m, 7.05–7.07 m, 7.13–7.15 m,
8. Burnett MN, Johnson CK. ORTEP III, Report ORNL-6895, Oak
7
.22–7.29 m, 7.35–7.38 m, 7.44–7.48 m, 7.86–7.87 m, 14.37
Ridge National Laboratory: Oak Ridge, 1996.
9. Pauling L. The Nature of Chemical Bond (3rd edn). Cornell
University Press: Ithaca, 1960.
1
3
brs. ( C NMR, 125.77 MHz, CDCl
3
): υ 20.82, 115.79, 119.10,
1
1
23.48, 124.91, 125.66, 129.49, 129.63, 129.82, 130.18, 134.66,
34.79, 135.95, 139.48, 139.70, 148.89, 160.01, 186.43. Form
10. Allen FH, Kennard O, Watson DG, Brammer L, Orpen AG,
Taylor R. J. Chem. Soc., Perkin Trans. 2 1987; S1.
1
B ( H NMR, 500.13 MHz, CDCl
3
): υ 2.25 s, 6.58–6.62 m,
11. Gilli G, Bellucci F, Ferretti V, Bertolasi V. J. Am. Chem. Soc. 1989;
6.97–6.98 m, 7.13–7.15 m, 7.35–7.38 m, 7.60–7.63 m, 7.70–
111: 1023.
1
3
7
.73 m, 7.79–7.80 m, 8.10–8.11 m, 13.27 brs. C NMR
): 20.72, 115.08, 118.57, 122.53, 128.57,
32.21, 133.39, 136.54, 139.10, 188.49. Anal. calc. for
O (339.39): C 77.86; H 5.05; N 12.38; found C 78.13;
H 5.07; N 12.32.
12. Gilli G, Gilli P. J. Mol. Struct. 2000; 552: 1.
13. Gilli P, Bertolasi V, Ferretti V, Gilli P. J. Am. Chem. Soc. 2000; 122:
(
125.77 MHz, CDCl
3
10 405.
1
1
1
1
1
4. Ly cˇ ka A. Collect. Czech. Chem. Commun. 1982; 47: 1112.
22 17 3
C H N
5. Ly cˇ ka A, Mach a´ cˇ ek V. Dyes Pigm. 1986; 7: 171.
ˇ
6. Ly cˇ ka A, Snobl D. Collect. Czech. Chem. Commun. 1981; 46: 892.
ˇ
7. Ly cˇ ka A, Snobl D, Mach a´ cˇ ek V, Ve cˇ e rˇ a M. Org. Magn. Reson.
3
2
-Phenyliminoindan-1,2-dione
1981; 16: 17.
15
15
ˇ
-(4-methylphenylhydrazone N ) (4a- N)
18. Ly cˇ ka A, Snobl D, Mach a´ cˇ ek V, Ve cˇ e rˇ a M. Org. Magn. Reson.
1981; 15: 390.
ˇ
The product was prepared in the same way as its 14N
1
2
9. Ly cˇ ka A, Jirman J, Mustroph H. Dyes Pigm. 1995; 28: 207.
0. Altomare A, Burla MC, Camalli M, Cascarano GL, Giacov-
azzo C, Guagliardi A, Moliterni AGG, Polidori G, Spagna R. J.
Appl. Crystallogr. 1999; 32: 115.
isotopomer. m.p. 173–176 °C. Yield 35%.
3
-Phenylimino-indan-1,2-dione 2-phenylhydrazone (4b)
2
1. Sheldrick GM. SHELX-97, Program for Crystal Structure
Refinement. University of Gottingen: Gottingen, Germany, 1997.
2. Nardelli M. J. Appl. Crystallogr. 1995; 28: 659.
This compound was prepared in the same way as its
methyl analog 4a. Product is brown-yellow crystallinic
compound, crystallization from ethanol, m.p. 190.5–192 °C.
Yield 58%. Form A ( H NMR, 500.13 MHz, CDCl
2
2
2
3. Farrugia L. J. Appl. Crystallogr. 1999; 32: 837.
4. Hideo I, Yuasa Y, Kibayashi Ch. J. Org. Chem. 1980; 45: 2938.
1
3
): υ
6.63 d, J D 8.0 Hz, 7.05–7.07 m, 7.09–7.11 m, 7.23–7.25 m,
25. Regitz M, Schwall H. Justus Liebigs Ann. Chim. 1969; 728: 104.
Copyright  2007 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2007; 45: 330–339
DOI: 10.1002/mrc